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From "Jonathan Gray" <jg...@apache.org>
Subject Re: Review Request: HBASE-2832: Priorities and multi-threading for MemStore flushing
Date Tue, 13 Jul 2010 05:40:44 GMT


> On 2010-07-12 21:55:02, stack wrote:
> > I like what this adds but I'm not mad about the foundation its built upon.  The
EventType stuff seems off to me.

Thanks for good review stack.

Let's get this event stuff right because it's a huge part of the master changes.


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/executor/HBaseEventHandler.java, line
20
> > <http://review.hbase.org/r/301/diff/2/?file=2551#file2551line20>
> >
> >     You couldn't call it EventHandler in the end?

Yup, we can.  Will be EventType/EventHandler with master changes.  Requires the rest of the
ZK cleanup to do the full changeover.


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/executor/HBaseEventHandler.java, line
41
> > <http://review.hbase.org/r/301/diff/2/?file=2551#file2551line41>
> >
> >     Does the base class have to know of all subclasses?
> >     
> >     http://download.oracle.com/docs/cd/E17409_01/javase/6/docs/api/java/beans/EventHandler.html
and http://download.oracle.com/docs/cd/E17409_01/javase/6/docs/api/java/util/EventObject.html
are not of use here?

Not sure what you're saying with java beans classes?  You want to reuse those?  These are
quite specialized.

We went over this stuff a few times when we did that big group review of that first master
zk patch.

Basically what we ended up doing was trying to keep the places things are tied together (handlers,
executors, types) in enums and in as few places as possible.  You add new executor service
types in the ExecutorService class, but otherwise all the declaring/connecting of these things
is done within HBaseEventHandler.


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/executor/HBaseEventHandler.java, line
52
> > <http://review.hbase.org/r/301/diff/2/?file=2551#file2551line52>
> >
> >     A Comparable Runnable?  Thats kinda odd?  Runnable is a faceless Interface..
has nothing but a run in it... how could it be comparable?  Should be Comparable<HBaseEventHandler>?

I tried a few different approaches to have prioritized stuff.

The underlying data structure expected by the java executor services are BlockingQueue<Runnable>.
 It's trivial then to make the actual queue a PriorityBlockingQueue<Runnable> which
then just requires whatever you put in there to implement Comparable<Runnable>.  In
the compareTo we know that we will only be compared to other HBaseEventHandlers, so we can
cast and do priority/FIFO comparisons.

I'm pretty open to other approaches (I did Comparable<HBaseEventHandler> in one attempt
already) but this turned out to be the cleanest.  Now the handlers need only override a single
getPriority() method rather than also be comparables themselves.

Being a Comparable<HBEventHandler> means we'll have to not use a java executor service
directly, or have two separate queues.  It always starts to get a bit awkward which is why
I ended up this way.


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/executor/HBaseEventHandler.java, line
151
> > <http://review.hbase.org/r/301/diff/2/?file=2551#file2551line151>
> >
> >     Why only this one handled in here?  All others in subclass?

hmm, not so?  this is only RS event right now.  method immediately above it, getMasterExecutorForEvent(),
is the same style and is already committed doing master open/close handlers.


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/executor/HBaseEventHandler.java, line
198
> > <http://review.hbase.org/r/301/diff/2/?file=2551#file2551line198>
> >
> >     Can you not use enums here?  RS_FLUSH_REGION.value rather than 64?  (where value
is datamember of the enum?)

case statements must use constants.  i could switch to else if?


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/executor/HBaseExecutorService.java,
line 78
> > <http://review.hbase.org/r/301/diff/2/?file=2552#file2552line78>
> >
> >     As above, this passed in int should be settting a data member (whats it setting
otherwise, the enum index?)

i'm not totally clear on this int stuff with the enums.  on the event types, we actually persist
them, so I understand wanting the byte/int value.  not sure here, we can just take it out?
 there is intValue/value in there.


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/executor/HBaseExecutorService.java,
line 157
> > <http://review.hbase.org/r/301/diff/2/?file=2552#file2552line157>
> >
> >     Whats this wait for 60 seconds about?  Hoping for an interrupt?  Why hardcoded?

Need to figure out what to do here.  Wait indefinitely?

Basically, we shutdown the executor services gracefully at first (we let running and submitted
tasks finish).  Then we'll wait for a certain period of time before interrupting the threads
running.

I felt like it was weird to wait indefinitely but this was the behavior previously.  I guess
I should set to 0?

(For example, MemStoreFlusher has a lock that prevents interruption while a flush is running,
so it's equivalent to a graceful shutdown)

I suppose there is a difference here which is this also includes items waiting in the queue.


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java, line
1032
> > <http://review.hbase.org/r/301/diff/2/?file=2555#file2555line1032>
> >
> >     Why ain't this FlushEventType.startExecutorService?  There are no master flushes
so why this RS stuff in here?

There is separation between what runs on master side and what runs on RS side.  Different
mapings.

This may not even be necessary anymore, there was some reason for the separation, need to
ask Karthik on this.


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreFlusher.java, line
270
> > <http://review.hbase.org/r/301/diff/2/?file=2556#file2556line270>
> >
> >     Whats up?  We just let the DroppedSnapshotException out now?  Or do we not throw
them anymore?

As per description, handling of this moved to FlushHandler.


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreFlusher.java, line
339
> > <http://review.hbase.org/r/301/diff/2/?file=2556#file2556line339>
> >
> >     Why would a FlushHandler take anything but a FlushRegionEventType enum?  Why
even pass it in?

It's not necessary for this one.  Some of the other events take multiple event types (for
example, we share a handler for opening/opened events).

Will clean that up.


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/regionserver/handler/FlushHandler.java,
line 76
> > <http://review.hbase.org/r/301/diff/2/?file=2557#file2557line76>
> >
> >     Your nice formatting here will not come out in javadoc.

throwing <pre> tags around it enough?


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/regionserver/handler/FlushHandler.java,
line 127
> > <http://review.hbase.org/r/301/diff/2/?file=2557#file2557line127>
> >
> >     Can these be final?

done


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/regionserver/handler/FlushHandler.java,
line 148
> > <http://review.hbase.org/r/301/diff/2/?file=2557#file2557line148>
> >
> >     Yeah, why does eventType have to be passed?  Once in here, you know what to
pass?

done


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/regionserver/handler/FlushHandler.java,
line 178
> > <http://review.hbase.org/r/301/diff/2/?file=2557#file2557line178>
> >
> >     If 1, 2, 3, you don't need to specify?  Just use enum ordinal?

yeah it does.  seemed clearer to have the ints here i think.  i have gone back and forth several
times and whether to have these ints in the enums or not, i'm not sure why i ended up with
all of them having it.

so you think it's better i completely remove the ints?  what about in EventHandler where we
persist it sometimes?


> On 2010-07-12 21:55:02, stack wrote:
> > trunk/src/main/java/org/apache/hadoop/hbase/regionserver/handler/FlushHandler.java,
line 220
> > <http://review.hbase.org/r/301/diff/2/?file=2557#file2557line220>
> >
> >     Low and high priority do same thing?

yup.  i had/have bigger plans to get rid of MemStoreFlusher so that FlushHandler actually
does the checks and stuff.  For now it's still in the MemStoreFlusher thread and just the
flushing is multi-threaded in here.

until that happens, same thing, that's why they call the same method, just a different log
message.

so they do the same flush but they carry a different priority so will be executed in priority
order.


- Jonathan


-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
http://review.hbase.org/r/301/#review377
-----------------------------------------------------------


On 2010-07-12 21:41:44, Jonathan Gray wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> http://review.hbase.org/r/301/
> -----------------------------------------------------------
> 
> (Updated 2010-07-12 21:41:44)
> 
> 
> Review request for hbase, stack, Karthik Ranganathan, and Kannan Muthukkaruppan.
> 
> 
> Summary
> -------
> 
> Adds support for priorities and concurrency to regionserver flushing.
> - Adds support for RS-side events/handlers/executors
> - Adds support for prioritized HBaseEventHandlers
> - Flushing now happens through FlushHandler, a new HBaseEventHandler.  There is an RS_FLUSHER
executor pool that defaults to two threads right now but is also checking a conf value.  There
is a good bit of documentation in FlushHandler.
> - Adds unit test TestFlushHandler.  There is a nicer way to detect when flushes finish
now for other tests.
> - Handling of FS errors is pushed into FlushHandler now.  The changes happening with
the master rewrite introduce a ServerStatus interface (probably a RegionStatus for rs side)
that will contain the necessary methods rather than using HRegionServer directly as is required
for now.
> - Something weird not passing in tests with multiple masters and regionservers, still
working that out.
> 
> 
> This addresses bug HBASE-2832.
>     http://issues.apache.org/jira/browse/HBASE-2832
> 
> 
> Diffs
> -----
> 
>   trunk/src/main/java/org/apache/hadoop/hbase/executor/HBaseEventHandler.java 963507

>   trunk/src/main/java/org/apache/hadoop/hbase/executor/HBaseExecutorService.java 963507

>   trunk/src/main/java/org/apache/hadoop/hbase/master/HMaster.java 963507 
>   trunk/src/main/java/org/apache/hadoop/hbase/regionserver/CompactSplitThread.java 963507

>   trunk/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java 963507

>   trunk/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreFlusher.java 963507

>   trunk/src/main/java/org/apache/hadoop/hbase/regionserver/handler/FlushHandler.java
PRE-CREATION 
>   trunk/src/test/java/org/apache/hadoop/hbase/regionserver/TestFlushHandler.java PRE-CREATION

> 
> Diff: http://review.hbase.org/r/301/diff
> 
> 
> Testing
> -------
> 
> Adds TestFlushHandler which passes.  Working on getting unit tests passing now, something
related to the ExecutorService.
> 
> 
> Thanks,
> 
> Jonathan
> 
>


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